1. Field of the Invention
The invention relates to a method for etching features, such as high aspect ratio features, into an etch layer.
2. Description of the Related Art
The present invention relates to the formation of semiconductor devices.
It is known to apply plasma excitation fields at two different frequencies to a region of a vacuum chamber for plasma processing a workpiece, wherein the region is coupled to a gas that the fields convert into the processing plasma. The workpiece is usually a semiconductor wafer, or dielectric plate and the plasma is involved in forming integrated circuit features on the workpiece. Typically, the plasma excitation fields at the two different frequencies are supplied to the region by a pair of spaced electrodes in the chamber or one electrode in the chamber and a reactance, in the form of a coil, located outside the chamber. The excited plasma typically dry etches the workpiece, but in some instances results in materials being deposited on the workpiece. High frequency RF power (having a frequency in excess of approximately 10 MHz) typically controls the density of the plasma, i.e., the plasma flux, while RF power having a low to medium frequency (in the range of 100 kHz to approximately 10 MHz) typically controls the energy of ions in the plasma and incident on the workpiece.
As the size of the features continues to decrease, there are increased requirements for precise control of various parameters of the plasma processing a workpiece. Amongst the plasma parameters requiring precise control are the plasma chemistry (i.e., types of ionic and radical species), the plasma flux and the ion energy of the plasma incident on the substrate. With the shrinking feature sizes and use of new materials in fabrication of integrated circuits, windows involved in processing the workpiece are decreasing in size, while pushing the limits on presently available plasma processors, particularly processors for etching. The shrinking feature sizes and requirements for new materials limit the use of the same reactor, i.e., vacuum processing chamber, for different etch applications.
High-aspect ratio (HAR) openings have a high opening depth to opening diameter ratio. A mask, such as a photoresist mask or a hard mask, is used to provide an opening pattern. In the specification and claims, a high aspect ratio feature is defined as a feature with a depth to diameter ratio greater than 10:1.
As the integrated circuit dimensions shrinks, the CDs and profile control along with the etch stop in high aspect ratio contact hole etching becomes very challenging problem in dielectric etch. The various features (top and bottom CD, profile angle, bowing and necking) of the contact/via hole depend upon plasma properties (e.g. plasma chemistry, ions to neutral flux, ion energy distribution etc.) and substrate properties (doping level of the dielectric material, temperature of the substrate etc.). However, for the same substrate properties, the plasma properties vary ( the ion to neutral ratio, the total flux etc.) as the high aspect ratio contact etching progresses. This causes a lower etch rate as the aspect ratio of the holes increases that leads to either etch stop or taper profile etc. Thus, the etching conditions has to be tailored to the etch depth and required profile providing an improved etch.